Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/38—Chromatising
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
  • B05D7/50—Multilayers
  • B05D7/51—One specific pretreatment, e.g. phosphatation, chromatation, in combination with one specific coating
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
  • C23C28/02—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings only including layers of metallic material
  • C23C28/023—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings only including layers of metallic material only coatings of metal elements only
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
  • C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
  • C23C28/32—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer
  • C23C28/322—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer only coatings of metal elements only
  • C23C28/3225—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer only coatings of metal elements only with at least one zinc-based layer
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
  • C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
  • C23C28/34—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one inorganic non-metallic material layer, e.g. metal carbide, nitride, boride, silicide layer and their mixtures, enamels, phosphates and sulphates
  • C23C28/345—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one inorganic non-metallic material layer, e.g. metal carbide, nitride, boride, silicide layer and their mixtures, enamels, phosphates and sulphates with at least one oxide layer
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D2350/00—Pretreatment of the substrate
  • B05D2350/60—Adding a layer before coating
  • B05D2350/65—Adding a layer before coating metal layer
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D2701/00—Coatings being able to withstand changes in the shape of the substrate or to withstand welding
  • B05D2701/30—Coatings being able to withstand changes in the shape of the substrate or to withstand welding withstanding bending
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/12—All metal or with adjacent metals
  • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
  • Y10T428/12535—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.] with additional, spatially distinct nonmetal component
  • Y10T428/12542—More than one such component
  • Y10T428/12549—Adjacent to each other
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/12—All metal or with adjacent metals
  • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
  • Y10T428/12535—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.] with additional, spatially distinct nonmetal component
  • Y10T428/12556—Organic component
  • Y10T428/12569—Synthetic resin

Definitions

• This invention relates to lubricating resin coated steel strips having improved formability and corrosion resistance and thus suitable for use in automobiles, electric appliances, and buildings.
• Steel strips or sheets more particularly plated steel strips such as zinc or zinc base alloy plated steel strips are often used in automobiles, electric appliances, buildings and the like with or without coating. Before coating, they must have passed a number of steps and are kept uncoated for a sustained length of time. During the process, often rust will occur and various deposits and debris will deposit and adhere to the surface of plated steel strips, both adversely affecting the adherence of a subsequently applied paint.
• the plated steel strips are chromate treated as a primary measure for protecting rust formation until they are used by the users.
• Ordinary chromate treatment can provide a limited degree of corrosion resistance which is as low as 24 to 48 hours as examined by a salt spray test.
• a special chromate treatment which is a coating chromate treatment using a chromate solution having silica sol added, can achieve an increased degree of corrosion resistance which is just 100 to 200 hours as examined by a salt spray test. This order of corrosion resistance, however, is insufficient for steel strips destined for long term service under a severe corrosive environment.
• lubricant oil is applied to steel strips before they are press formed.
• the process must be followed by degreasing. Therefore, there is a need for surface-treated steel strips which can be press formed without applying lubricant oil.
• Japanese Patent Publication No. 24505/1987 discloses a dual coated chromate steel strip having improved corrosion resistance and lubricity comprising a chromate coating on a zinc-base alloy plated steel substrate and a layer thereon of a urethane-modified epoxy resin containing composite aluminum phosphate, a chromium base anti-rust pigment, and a lubricant selected from polyolefin wax, molybdenum disulfide, and silicone.
• the coating weight of the resin layer is from 1 to 10 g/m 2 .
• Japanese Patent Application Kokai No. 35798/1988 discloses an organic coated steel strip having improved cationic electro-deposition capability comprising a chromate coating on a zinc-base alloy plated steel substrate and a layer thereon of a urethane-modified epoxy ester resin containing silica powder, a hydrophilic polyamide resin, and a polyethylene wax lubricant.
• the resin layer has a thickness of 0.3 to 5 ⁇ m.
• Japanese Patent Application Kokai No. 73938/1987 discloses a corrosion resistant coated laminate comprising a steel substrate having a gamma-phase monolayer of nickel-containing zinc plated thereon, a chromate coating thereon, and a coating thereon containing a base resin, iron phosphide conductive pigment, and a lubricant selected from polyolefins, carboxylate esters, and polyalkylene glycols.
• the resin coating has a thickness of 1 to 20 ⁇ m.
• These three types of surface-treated steel strip are dual coated steel strips having improved corrosion resistance and lubricity characterized by having a lubricating resinous coating containing a polyolefin lubricant on the chromate coating.
• a primary object of the present invention is to provide a novel and improved surface-treated steel strip which can be continuously press formed at high speeds.
• Another object of the present invention is to provide such a surface-treated steel strip which can be press formed without application of lubricant.
• a further object of the present invention is to provide such a surface-treated steel strip which is resistant to stains as by fingerprints during handling.
• Still another object of the present invention is to provide such a surface-treated steel strip having improved continuous deep drawability.
• Yet another object of the present invention is to provide such a surface-treated steel strip having improved corrosion resistance.
• a lubricating resin coated steel strip having improved formability comprising
• chromate coating on each surface of the substrate, the chromate coatings each having a coating weight of up to 200 mg/m 2 of metallic chromium, and
• the resin coatings being formed from a resin composition comprising
• the resin composition having a glass transition temperature Tg of at least 70° C., the resin coatings each having a dry coating weight of 0.3 to 3 gram/m 2 .
• the resin composition contains as component (c) a mixture of a polyolefin wax having a melting point of lower than 70° C. and a polyolefin wax having a melting point of at least 70° C.
• the former wax is up to 70% by weight of the mixture.
• a lubricating resin coated steel strip having improved corrosion resistance comprising
• chromate coatings on each surface of the substrate, the chromate coatings each having a coating weight of 10 to 200 mg/m 2 as Cr and
• the resin coatings being formed from a resin composition comprising
• the resin composition having a glass transition temperature Tg of at least 70° C., the resin coatings each having a dry coating weight of 0.3 to 3 gram/m 2 .
• the resin composition further comprises (d) a polyolefin wax having a melting point of at least 70° C., the weight ratio of polyolefin wax to fluoro resin being up to 1.0.
• the powder fluoro resin has a particle size of 1 to 7 ⁇ m.
• the resin composition further comprises (e) a silane coupling agent.
• a lubricating resin coated steel strip having improved formability and corrosion resistance comprising a steel substrate having zinc, a zinc base alloy or an aluminum base alloy plated on each surface thereof, and chromate coatings on both surfaces of the substrate.
• a resin coating is formed on one of the chromate coatings from a resin composition comprising (a) a resin having a hydroxyl and/or carboxyl group, (b) silica, and (c) a solid lubricant and having a glass transition temperature Tg of at least 70° C.
• Another resin coating is formed on the other chromate coating from a resin composition comprising (a) a resin having a hydroxyl and/or carboxyl group and (b) silica.
• Each of the resin coatings having a dry coating weight of 0.3 to 3 gram/m 2 .
• the solid lubricant comprises a fluoro resin or a polyolefin compound having a melting point of at least 70° C. More preferably, the solid lubricant comprises a mixture of a fluoro resin and a polyolefin compound.
• All the lubricating resin coated steel strips according to the present invention are based on the same types of steel stock including steel strips or sheets having zinc, a zinc base alloy or an aluminum base alloy plated on both surfaces thereof.
• Examples of the starting steel include zinc electroplated steel, zinc-nickel electroplated steel, zinc hot dipped steel, and 5% aluminum-zinc hot dipped steel.
• a typical example of aluminum base alloy for plating is an aluminum-zinc alloy containing more than 50% by weight of aluminum.
• the starting steel stock is sometimes referred to as zinc plated steel since all these platings contain zinc.
• the chromate coatings on both surfaces of the zinc plated steel substrate are also common to all the lubricating resin coated steel strips according to the present invention in any aspects.
• the chromate coatings may be conventional well-known ones.
• zinc plated steel on both surfaces may be treated with a chromate treating solution, for example, an aqueous solution containing chromic anhydride, a chromate salt, dichromic acid or the like as an active ingredient or a solution containing colloidal silica in such an aqueous solution by conventional well-known procedures.
• a chromate coating predominantly comprising hydrated chromium oxides.
• the lubricating resin coated steel strip having improved press formability according to the first embodiment of the present invention is described.
• the steel strip in the first form has an organic resin coating of the following composition and coating weight on each of the chromate coatings as described above.
• the organic resin coatings on opposite sides are generally the same.
• the resin coatings are formed from a resin composition comprising
• a solid lubricant in the form of a polyolefin wax having a melting point of at least 70° C. or a mixture of a polyolefin wax having a melting point of lower than 70° C. and a polyolefin wax having a melting point of at least 70° C.
• the resin composition has a glass transition temperature Tg of at least 70° C.
• Each of the resin coatings has a coating weight of 0.3 to 3.0 gram/m 2 on a dry basis.
• the base resin used in the lubricating resin composition is a resin having a hydroxyl group or a carboxyl group or both hydroxyl and carboxyl groups.
• the base resin include epoxy resins, alkyd resins, acrylic resins, urethane resins, phenolic resins, melamine resins, and polyvinyl butyral resins.
• the resins having a hydroxyl group and/or a carboxyl group are effective for the following reason.
• the lubricating resin coated steel strip in the first form is provided with an inorganic-organic composite coating of silica and resin for the purpose of improving corrosion resistance.
• Hydroxyl and carboxyl groups are desirable as the active group capable of reacting with hydroxyl groups on the silica surface to form a highly corrosion resistant film.
• Silica is blended for the purpose of improving the corrosion resistance of the lubricating resin coated steel strip.
• colloidal silicas such as Snowtex-O and Snowtex-N (both manufactured by Nissan Chemical K.K.), organosilica sols such as ethyl cellosolve silica sol available from Nissan Chemical K.K., silica powder such as gas phase silica powder available from Aerogel K.K., and organic silicates such as ethyl silicate.
• the powder silica preferably has a particle size of 5 to 70 nm for uniform dispersion.
• a silane coupling agent may be included as a promoter for enhancing reaction between the base resin and silica.
• the silane coupling agent include ⁇ -(2-aminoethyl)aminopropyltrimethoxysilane and ⁇ -glycidoxypropyltrimethoxy-silane.
• Any commonly used additives including reaction promoters, stabilizers and dispersants may be blended with the base resin without detracting from the effectiveness of the present invention. Blending of such additives is often desirable.
• various dry lubricants including wax, molybdenum disulfide, organic molybdenum compounds, graphite, carbon fluorides, metal soap, boron nitride and fluoro resins. These materials are used as lubricants for bearings or added to plastics, oil, grease or the like for improving lubricity. Using these dry lubricants, we attempted to produce resin coated steel strips having good lubricity.
• organic lubricants having a relatively high melting point and a relatively low specific gravity can meet the above-mentioned requirements and inter alia, a polyolefin wax having a melting point of at least 70° C. (to be referred to as high-melting, hereinafter) is a useful lubricant.
• strips are heated to high temperatures on their surface in frictional contact with the die or punch. At this point, the high-melting polyolefin wax performs well as the lubricant.
• Strips become hot on their surface in frictional contact with the die or punch during the high-speed press forming process as described above.
• the use of the high-melting polyolefin wax which exerts good lubricity at high temperatures is, of course, effective in improving lubricity.
• the addition of low-melting polyolefin wax which is a good lubricant at room temperature assists in improving lubricity even at the initial.
• the low-melting polyolefin wax serves at the initial stage and the high-melting polyolefin wax serves at intermediate to final stages. Lubricity is thus improved throughout the press forming process.
• the strip temperature quickly increases at the very initial stage of forming and since there is little possibility that the strip be broken within a very short time when the strip remains at room temperature, addition of only the high-melting polyolefin wax can provide sufficient lubricity.
• addition of the low-melting polyolefin wax has another advantage of improving the dispersion of the wax in the base resin.
• the polyolefin wax may be selected from polymers of olefinic hydrocarbons, for example, polyethylene, polypropylene, and polybutene.
• the chromate coating on each surface may have a coating weight of up to 200 mg/m 2 as Cr. Coating weights of more than 200 mg/m 2 are no longer advantageous for various reasons. Further improvement in corrosion resistance is less expectable for increments of coating weight.
• the chromate treating solution is drastically exhausted to render the surface appearance poor. In addition, thicker chromate coatings will adversely affect press formability.
• the resin composition in the form of a resin mixture or resin composite contains specific proportions of the essential components, base resin, silica, and polyolefin wax.
• the silica which is used for the purpose of improving corrosion resistance is added in an amount of 10 to 80 parts by weight per 100 parts by weight of the resin having a hydroxyl and/or carboxyl group. Less than 10 parts by weight of silica is less effective for corrosion resistance improvement. More than 80 parts by weight of silica forms a hard film which is prone to galling, lowering press formability.
• the polyolefin wax or lubricity imparting agent is added in an amount of up to 20 parts by weight per 100 parts by weight of the resin having a hydroxyl and/or carboxyl group for both cases where the polyolefin wax is solely of the high-melting type or a mixture of the high- and low-melting types. More than 20 parts by weight of the polyolefin wax forms a weak resin coating which is less lubricating.
• the proportion of the high- and low-melting types is such that the low-melting polyolefin wax is up to 70% by weight of the mixture.
• the above-mentioned essential components are blended in the above-defined proportions so as to form a resin composition having a Tg of at least 70° C. while any other desired additives may also be blended.
• Resin composition coatings having a Tg of lower than 70° C. tend to soften and separate from the underlying chromate coating when the worked surface of the associated strip becomes hot during high-speed press forming. Peeling of resin coatings causes resin fragments to deposit on the die and disturbs continuous press forming. The outside appearance of pressed articles is poor because of such powdering.
• the lubricating resin coating on each surface of the strip has a weight of 0.3 to 3.0 grams per square meter (gram/m 2 ) on a dry basis. Resin coatings of less than 0.3 gram/m 2 are too thin to smooth out irregularities on the chromated steel strip or to provide corrosion resistance. Thicker coatings of more than 3.0 gram/m 2 show enhanced corrosion resistance, but detract from press formability, powdering resistance and economy.
• the starting stock for the lubricating resin coated steel strip may be selected from steel strips having zinc, a zinc base alloy or an aluminum base alloy plated on both surfaces thereof, for example, zinc electroplated steel, zinc-nickel electroplated steel, zinc hot dipped steel, and 5% aluminum-zinc hot dipped steel.
• Chromate coatings are then applied to both surfaces of the zinc plated steel substrate by any conventional well-known procedures.
• dipping or electrolytic chromate treatment may be carried out on zinc plated steel in an aqueous solution containing chromic anhydride, a chromate salt, dichromic acid or the like as an active ingredient.
• coating chromate treatment may be carried out on zinc plated steel by applying a solution containing colloidal silica in the above-mentioned aqueous chromate solution to the strip steel. There results a chromate coating predominantly comprising hydrated chromium oxides.
• treatment of zinc plated steel with a chromate solution is followed by squeezing between flat rubber rolls or drying as by hot air blowing, thus forming chromate coatings on both surfaces of the steel strip.
• the resin composition is prepared by providing necessary amounts of the essential components and optional additives and mixing them into a physically uniform dispersion.
• a silane coupling agent is preferably added to the dispersion, which is further milled into a physically uniform mixture or composite composition.
• the resin composition is then applied to the chromated steel by any conventional well-known techniques such as roll coating, spraying, dipping, and brush coating to a predetermined thickness.
• the coatings are generally dried at a temperature of 80° to 180° C. for about 3 to about 90 seconds.
• the lubricating resin coated steel strip having improved formability according to the first embodiment is produced in this way.
• the lubricating resin coated steel strip having improved corrosion resistance according to the second embodiment of the present invention is described.
• the steel strip in the second form has an organic resin coating of the following composition and coating weight on each of the chromate coatings as described above.
• the organic resin coatings on opposite sides are generally the same.
• the resin coatings are formed from a resin composition comprising
• the resin composition has a glass transition temperature Tg of at least 70° C.
• Each of the resin coatings has a coating weight of 0.3 to 3.0 gram/m 2 on a dry basis.
• the resin coatings are formed from a resin composition comprising
• the resin composition has a glass transition temperature Tg of at least 70° C.
• Each of the resin coatings has a coating weight of 0.3 to 3.0 gram/m 2 on a dry basis.
• the base resin used in the lubricating resin composition is a resin having a hydroxyl group or a carboxyl group or both hydroxyl and carboxyl groups.
• the base resin include epoxy resins, alkyd resins, acrylic resins, urethane resins, phenolic resins, melamine resins, and polyvinyl butyral resins.
• the resins having a hydroxyl group and/or a carboxyl group are effective for the following reason.
• the lubricating resin coated steel strip in the second form is provided with an inorganic-organic composite coating of silica and resin for the purpose of improving corrosion resistance.
• Hydroxyl and carboxyl groups are desirable as the active group capable of reacting with hydroxyl groups on the silica surface to form a highly corrosion resistant film.
• Silica is blended for the purpose of improving the corrosion resistance of the lubricating resin coated steel strip.
• colloidal silicas such as Snowtex-O and Snowtex-N (both manufactured by Nissan Chemical K.K.), organosilica sols such as ethyl cellosolve silica sol available from Nissan Chemical K.K., silica powder such as gas phase silica powder available from Aerogel K.K., and organic silicates such as ethyl silicate.
• the powder silica preferably has a particle size of 5 to 70 nm for uniform dispersion.
• a silane coupling agent may be included as a promoter for enhancing reaction between the base resin and silica.
• the silane coupling agent include ⁇ -(2-aminoethyl)aminopropyltrimethoxysilane and ⁇ -glycidoxypropyltrimethoxysilane.
• Any commonly used additives including reaction promoters, stabilizers and dispersants may be blended with the base resin without detracting from the effectiveness of the present invention. Blending of such additives is often desirable.
• various dry lubricants including wax, molybdenum disulfide, organic molybdenum compounds, graphite, carbon fluorides, metal soap, boron nitride and fluoro resins. These materials are used as lubricants for bearings or added to plastics, oil, grease or the like for improving lubricity. Using these dry lubricants, we attempted to produce resin coated steel strips having good lubricity.
• organic lubricants having a relatively high melting point and a relatively low specific gravity can meet the above-mentioned requirements and inter alia, a powder fluoro resin is a useful lubricant and has an additional advantage of corrosion resistance improvement.
• Non-limiting examples of the fluoro resin include a polytetrafluoroethylene resin, polyvinyl fluoride resin, polyvinylidene fluoride resin, polyfluoroethylene resin, and a mixture of two or more of them.
• the powder fluoro resin may have a particle size of at least about 0.1 ⁇ m. It has been found that relatively large fluoro resin particles protruding beyond the resin coating are effective to accommodate friction and impact with the die or punch during press forming. Fluoro resins having a particle size of 1 to 7 ⁇ m are thus advantageous for resin coatings having a coating weight of 0.3 to 3 gram/m 2 . Resin coatings containing fluoro resin with such a particle size can withstand severe working conditions as encountered when the blank holder pressure is increased above the ordinary level and the die or punch shoulder radius is reduced below the ordinary value.
• polyolefin wax having a melting point of at least 70° C.
• the polyolefin wax assists in dispersion of the fluoro resin in the base resin such that the fluoro resin may exert its lubricity to a greater extent.
• the polyolefin wax may be selected from polymers of olefinic hydrocarbons, for example, polyethylene, polypropylene, and polybutene as long as they have a melting point of at least 70° C.
• a polyolefin wax having a melting point of lower than 70° C. is less effective for continuous high-speed press forming.
• the chromate coating on each surface may have a coating weight of 10 to 200 mg/m 2 as Cr. Coating weights of less than 10 mg/m 2 are too thin to achieve corrosion resistance. Coating weights of more than 200 mg/m 2 are no longer advantageous for various reasons. Further improvement in corrosion resistance is less expectable for increments of coating weight.
• the chromate treating solution is drastically exhausted to render the surface appearance poor. In addition, thicker chromate coatings will adversely affect press formability.
• the resin composition in the form of a resin mixture or resin composite contains specific proportions of the essential components, base resin, silica, and fluoro resin and optional components such as polyolefin wax.
• the silica which is used for the purpose of improving corrosion resistance is added in an amount of 10 to 80 parts by weight per 100 parts by weight of the resin having a hydroxyl and/or carboxyl group. Less than 10 parts by weight of silica is less effective for corrosion resistance improvement. More than 80 parts by weight of silica forms a hard film which is prone to galling, lowering press formability.
• the powder fluoro resin or lubricity imparting agent is added in an amount of 1.0 to 20 parts by weight per 100 parts by weight of the resin having a hydroxyl and/or carboxyl group. Less than 1.0 parts by weight of fluoro resin is too small to provide lubricity or press formability. More than 20 parts by weight of fluoro resin forms a weak resin coating which is readily damaged with a loss of corrosion resistance after working.
• the polyolefin wax or secondary lubricity imparting agent is blended with the fluoro resin such that the weight ratio of polyolefin wax to fluoro resin is up to 1/1. With such weight ratios in excess of 1/1, there results a weak resin coating which cannot take full advantage of the lubricating nature of the fluoro resin.
• the above-mentioned essential and optional components are blended in the above-defined proportions so as to form a resin composition having a Tg of at least 70° C. while any other desired additives may also be blended.
• Resin composition coatings having a Tg of lower than 70° C. tend to soften and separate from the underlying chromate coating when the worked surface of the associated strip becomes hot during high-speed press forming. Peeling of resin coatings causes resin fragments to deposit on the die and disturbs continuous press forming. The outside appearance of pressed articles is poor because of such powdering.
• the lubricating resin coating on each surface of the strip has a weight of 0.3 to 3.0 grams per square meter (gram/m 2 ) on a dry basis. Resin coatings of less than 0.3 gram/m 2 are too thin to smooth out irregularities on the chromated steel strip or to provide corrosion resistance. Thicker coatings of more than 3.0 gram/m 2 show enhanced corrosion resistance, but detract from press formability, powdering resistance and economy.
• the starting stock for the lubricating resin coated steel strip may be selected from zinc plated steel strips, that is, steel strips having zinc, a zinc base alloy or an aluminum base alloy plated on both surfaces thereof, for example, zinc electroplated steel, zinc-nickel electroplated steel, zinc hot dipped steel, and 5% aluminum-zinc hot dipped steel.
• Chromate coatings are then applied to both surfaces of the zinc plated steel substrate by any conventional well-known procedures.
• dipping or electrolytic chromate treatment may be carried out on zinc plated steel in an aqueous solution containing chromic anhydride, a chromate salt, dichromic acid or the like as an active ingredient.
• coating chromate treatment may be carried out on zinc plated steel by applying a solution containing colloidal silica in the above-mentioned aqueous chromate solution to the strip steel. There results a chromate coating predominantly comprising hydrated chromium oxides.
• treatment of zinc plated steel with a chromate solution is followed by squeezing between flat rubber rolls or drying as by hot air blowing, thus forming chromate coatings on both surfaces of the steel strip.
• organic resin coatings are formed on both the chromate coatings as described above by applying the following composition to a coating weight of 0.3 to 3.0 gram/m 2 on a dry basis for each side.
• the resin composition used herein contains (a) 100 parts by weight of a resin having a hydroxyl and/or carboxyl group, (b) 10 to 80 parts by weight of silica, and (c) 1.0 to 20 parts by weight of a solid lubricant in the form of a powder fluoro resin and has a glass transition temperature Tg of at least 70° C.
• the other resin composition also used herein contains (a) 100 parts by weight of a resin having a hydroxyl and/or carboxyl group, (b) 10 to 80 parts by weight of silica, (c) 1.0 to 20 parts by weight of a solid lubricant in the form of a powder fluoro resin, and (d) a polyolefin wax having a melting point of at least 70° C., the weight ratio of the polyolefin wax to the fluoro resin being up to 1/1, and has a glass transition temperature Tg of at least 70° C.
• any commonly used additives such as reaction promoters, stabilizers and dispersants.
• Organic resin coatings may be formed on both the chromate coatings from the above-mentioned resin composition by the following procedure.
• the resin composition is formulated by preparing necessary amounts of the essential components and optional additives and mixing them into a physically uniform dispersion.
• a silane coupling agent is preferably added to the dispersion, which is further milled into a physically uniform mixture or composite composition.
• the resin composition is then applied to the chromated steel by any conventional well-known techniques such as roll coating, spraying, dipping, and brush coating to a predetermined thickness.
• the coatings are generally dried at a temperature of 80° to 180° C. for about 3 to about 90 seconds.
• the lubricating resin coated steel strip having improved corrosion resistance according to the second embodiment is produced in this way.
• the lubricating resin coated steel strip having improved formability and corrosion resistance according to the third embodiment of the present invention is described.
• the steel strip in the third form has different organic resin coatings on opposite sides. That is, an organic resin coating of the following composition and coating weight is on one of the chromate coatings as described above and another organic resin coating of the following composition and coating weight is on the other chromate coating.
• the resin coating on one side is formed from a resin composition comprising
• This resin coating has a coating weight of 0.3 to 3.0 gram/m 2 on a dry basis.
• the other resin coating on the opposite side is formed from a solid lubricant-free resin composition
• a solid lubricant-free resin composition comprising
• This resin coating has a coating weight of 0.3 to 3.0 gram/m 2 on a dry basis.
• the base resin used in the lubricating resin composition is a resin having a hydroxyl group or a carboxyl group or both hydroxyl and carboxyl groups.
• the base resin include epoxy resins, alkyd resins, acrylic resins, urethane resins, phenolic resins, melamine resins, and polyvinyl butyral resins.
• the resins having a hydroxyl group and/or a carboxyl group are effective for the following reason.
• the lubricating resin coated steel strip in the second form is provided with an inorganic-organic composite coating of silica and resin for the purpose of improving corrosion resistance.
• Hydroxyl and carboxyl groups are desirable as the active group capable of reacting with hydroxyl groups on the silica surface to form a highly corrosion resistant film.
• Silica is blended for the purpose of improving the corrosion resistance of the lubricating resin coated steel strip.
• colloidal silicas such as Snowtex-O and Snowtex-N (both manufactured by Nissan Chemical K.K.), organosilica sols such as ethyl cellosolve silica sol available from Nissan Chemical K.K., silica powder such as gas phase silica powder available from Aerogel K.K., and organic silicates such as ethyl silicate.
• the powder silica preferably has a particle size of 5 to 70 nm for uniform dispersion.
• a silane coupling agent may be included as a promoter for enhancing reaction between the base resin and silica.
• the silane coupling agent include ⁇ -(2-aminoethyl)aminopropyltrimethoxysilane and ⁇ -glycidoxypropyltrimethoxysilane.
• Any commonly used additives including reaction promoters, stabilizers and dispersants may be blended with the base resin without detracting from the effectiveness of the present invention. Blending of such additives is often desirable.
• various dry lubricants including wax, molybdenum disulfide, organic molybdenum compounds, graphite, carbon fluorides, metal soap, boron nitride and fluoro resins. These materials are used as lubricants for bearings or added to plastics, oil, grease or the like for improving lubricity. Using these dry lubricants, we attempted to produce resin coated steel strips having good lubricity.
• organic lubricants having a relatively high melting point and a relatively low specific gravity can meet the first-mentioned requirement and inter alia, powder fluoro resins and polyolefin compounds having a melting point of at least 70° C. are useful solid lubricants.
• the powder fluoro resins are particularly preferred since they have an additional advantage of corrosion resistance improvement. Better lubricity is achieved when a mixture of a fluoro resin and a polyolefin compound is used.
• Non-limiting examples of the fluoro resin include a polytetrafluoroethylene resin, polyvinyl fluoride resin, polyvinylidene fluoride resin, polyfluoroethylene resin, and a mixture of two or more of them.
• the powder fluoro resin may have a relatively small particle size, preferably up to about 10 ⁇ m. Resin compositions containing fluoro resin particles of a larger size are difficult to coat evenly. Fluoro resins having a particle size of 1 to 7 ⁇ m are advantageous for the same reason as previously described in the second embodiment.
• the polyolefin compound may be selected from polymers of olefinic hydrocarbons, for example, polyethylene, polypropylene, and polybutene.
• polyolefin compound is a sole lubricant in the resin composition
• strips are heated to high temperatures on their surface in frictional contact with the die or punch.
• use of the high-melting polyolefin which exerts good lubricity at such high temperatures is effective in improving lubricity.
• the lubricant consists solely of a polyolefin having a melting point of lower than 70° C. (low-melting polyolefin), it melts into liquid due to a temperature rise at the worked surface during high-speed press forming. The molten lubricant will flow away from the strip surface causing a local lack of lubricant, or adhere to the worked steel or die, adversely affecting continuous press forming and the outer appearance of the product.
• Strips become hot on their surface in frictional contact with the die or punch during the high-speed press forming process as described above.
• the use of the high-melting polyolefin compound which exerts good lubricity at high temperatures is, of course, effective in improving lubricity.
• the addition of low-melting polyolefin compound which is a good lubricant at room temperature assists in improving lubricity even at the initial.
• the low-melting polyolefin compound serves at the initial stage and the high-melting polyolefin compound serves at intermediate to final stages. Lubricity is thus improved throughout the press forming process.
• the low-melting polyolefin is believed to improve the dispersion of the polyolefins in the base resin, thus providing a uniform frictional resistance between the coated steel strip and the die during press forming for further enhanced lubricity.
• the lubricant used is a mixture of a powder fluoro resin and a polyolefin compound
• they can be selected from the above-mentioned fluoro resins and low- and high-melting polyolefin compounds.
• the use of a mixture of a powder fluoro resin and a polyolefin compound has the advantage that the polyolefin compound assists in dispersion of the powder fluoro resin in the base resin so that the fluoro resin may exert its lubricity to a greater extent.
• the resin coating on one surface of the chromated steel strip is formed from a resin composition containing (a) a base resin, (b) silica, (c) a solid lubricant, and any other optional additive(s) in such proportions that the composition has a Tg of at least 70° C. whereas the other resin coating on the opposite surface of the chromated steel strip is formed from a resin composition containing (a) a base resin, (b) silica, and any other optional additive(s).
• the resin composition has a Tg of at least 70° C.
• Resin composition coatings having a Tg of lower than 70° C. tend to soften and separate from the underlying chromate coating when the worked surface of the associated strip becomes hot during high-speed press forming. Peeling of resin coatings causes resin fragments to deposit on the die and disturbs continuous press forming. The outside appearance of pressed articles is poor because of such powdering.
• the lubricating resin coating on the one surface of the strip has a weight of 0.3 to 3.0 gram/m 2 on a dry basis. Resin coatings of less than 0.3 gram/m 2 are too thin to smooth out irregularities on the chromated steel strip or to provide corrosion resistance. Thicker coatings of more than 3.0 gram/m 2 show enhanced corrosion resistance, but detract from press formability, weldability, and economy.
• the lubricant-free resin coating on the other surface of the strip has a weight of 0.3 to 3.0 gram/m 2 on a dry basis for similar reasons.
• the resin coated steel strip of the third embodiment is preferably press formed at high speeds by placing it in a press such that the lubricating resin coating is on the side of the die and the lubricant-free resin coating is on the side of the punch. Deep drawability is expectable with this arrangement for the following reason.
• the coating on the die side has high lubricity and hence, low frictional resistance or drawing resistance whereas the coating on the punch side has low lubricity and hence, high frictional resistance or rupture resistance. This differential frictional resistance between the opposite coatings expedites deep drawing.
• the chromate coating on each surface is not particularly limited in coating weight in a broader sense, but may preferably have a coating weight of 10 to 200 mg/m 2 as Cr. Coating weights of less than 10 mg/m 2 are too thin to achieve corrosion resistance. Coating weights of more than 200 mg/m 2 are no longer advantageous for various reasons. Further improvement in corrosion resistance is less expectable for increments of coating weight.
• the chromate treating solution is drastically exhausted to render the surface appearance poor. In addition, thicker chromate coatings will adversely affect press formability.
• the resin composition in the form of a resin mixture or resin composite preferably contains specific proportions of the essential components.
• the lubricant-free resin composition contains a base resin and silica whereas the lubricating resin composition contains a base resin, silica, and a solid lubricant (fluoro resin and/or polyolefin).
• the silica which is used for the purpose of improving corrosion resistance is preferably added in an amount of 10 to 80 parts by weight per 100 parts by weight of the resin having a hydroxyl and/or carboxyl group. Less than 10 parts by weight of silica is less effective for corrosion resistance improvement. More than 80 parts by weight of silica forms a hard film which is prone to galling, lowering press formability.
• the powder fluoro resin or lubricity imparting agent is preferably added in an amount of 1.0 to 20 parts by weight per 100 parts by weight of the resin having a hydroxyl and/or carboxyl group. Less than 1.0 parts by weight of fluoro resin is too small to provide lubricity or press formability. More than 20 parts by weight of fluoro resin forms a weak resin coating which is readily damaged with a loss of corrosion resistance after working.
• the polyolefin compound when it is used as a sole lubricity imparting agent, is preferably added in an amount of 1.0 to 20 parts by weight per 100 parts by weight of the resin having a hydroxyl and/or carboxyl group.
• the weight ratio of low/high-melting polyolefin is preferably up to 5/2. Less than 1.0 parts by weight of the polyolefin compound is too short for lubricity. More than 20 parts by weight of the polyolefin compound forms a weak resin coating which is readily damaged and fails to maintain post-working corrosion resistance. A weight ratio of low/high-melting polyolefin of more than 5/2 will render a resin coating susceptible to damages and finally lead to reduced post-working corrosion resistance and blocking properties of the associated steel strip.
• the lubricity imparting agent is a mixture of a powder fluoro resin and a polyolefin compound
• the powder fluoro resin is preferably added in an amount of 1.0 to 20 parts by weight per 100 parts by weight of the resin having a hydroxyl and/or carboxyl group.
• the polyolefin compound is blended with the fluoro resin such that the weight ratio of polyolefin to fluoro resin is up to 1/1. With such weight ratios in excess of 1/1, there results a weak resin coating which cannot take full advantage of the lubricating nature of the fluoro resin.
• the starting stock for the lubricating resin coated steel strip may be selected from zinc plated steel strips, that is, steel strips having zinc, a zinc base alloy or an aluminum base alloy plated on both surfaces thereof, for example, zinc electroplated steel, zinc-nickel electroplated steel, zinc hot dipped steel, and 5% aluminum-zinc hot dipped steel.
• Chromate coatings are then applied to both surfaces of the zinc plated steel substrate by any conventional well-known procedures.
• dipping or electrolytic chromate treatment may be carried out on zinc plated steel in an aqueous solution containing chromic anhydride, a chromate salt, dichromic acid or the like as an active ingredient.
• coating chromate treatment may be carried out on zinc plated steel by applying a solution containing colloidal silica in the above-mentioned aqueous chromate solution to the strip steel. There results a chromate coating predominantly comprising hydrated chromium oxides.
• treatment of zinc plated steel with a chromate solution is followed by squeezing between flat rubber rolls or drying as by hot air blowing, thus forming chromate coatings on both surfaces of the steel strip.
• two different organic resin coatings are formed on the opposite chromate coatings as described above by applying the following compositions to a coating weight of 0.3 to 3.0 gram/m 2 on a dry basis for each side.
• Organic resin coatings may be formed on the chromate coatings from the above-mentioned resin compositions by the following procedure.
• the resin compositions are formulated by preparing necessary amounts of the essential components and optional additives and mixing them into physically uniform dispersions.
• a silane coupling agent is preferably added to the dispersions, which are further milled into physically uniform mixture or composite compositions.
• Each of the resin compositions is then applied to the chromated steel by any conventional well-known techniques such as roll coating, spraying, dipping, and brush coating to a predetermined thickness.
• the coatings are generally dried at a temperature of 80° to 180° C. for about 3 to about 90 seconds.
• the lubricating resin coated steel strip having improved formability and corrosion resistance according to the third embodiment is produced in this way.
• the resin coated.steel strip of the third embodiment is preferably press formed at high speeds by placing it in a press such that the lubricating resin coating is on the die side and the lubricant-free resin coating is on the punch side.
• Lubricating resin coated steel strips designated sample Nos. 101 to 117 were prepared under the following conditions.
• Zinc plating 20 gram/m 2
• Zinc-nickel plating 20 gram/m 2
• Nickel content 12% by weight
• Zinc plating 60 gram/m 2
• a chromate treating solution containing 20 gram/liter of CrO 3 and 4 gram/liter of Na 3 AlF 6 was spray coated to both surfaces of each of the above-identified steel strips.
• the sprayed strips were passed between flat rubber rolls for squeezing and dried by blowing hot air.
• the amount of chromate coating deposited was controlled to the values reported in Table 1 (up to 200 mg/m 2 as Cr on each side) by adjusting the spraying time.
• Coating dispersions having the composition reported in Table 1 were applied to both the surfaces of the chromated strips by roll coating, and dried at 150° C. for 40 seconds, forming resin coatings each having a coating weight of 0.3 to 3.0 gram/m 2 .
• sample Nos. 118 to 129 were prepared by the same procedures as above except that some parameters were outside the scope of the present invention. Plated steel strips were subjected to chromate treatment and coating dispersions having the composition reported in Table 1 were then applied to both the surfaces of the chromated strips to form resin coatings in the coating weights reported in Table 1.
• the Erichsen deep drawing cup test was carried out. Specimens of the same lot were deep drawn without lubricant oil by an Erichsen deep drawing machine while varying the drawing ratio, determining the limiting drawing ratio. At the same time, the powdering resistance was evaluated by collecting powdery deposits on the die (resulting from peeling of the resin coating) using adhesive tape.
• Drawing speed 5 mm/sec. and 500 mm/sec.
• a salt spray test was carried out according to JIS Z-2371 to measure the testing time until white rust occurred.
• Specimens were deep drawn without lubricant oil by an Erichsen cup drawing machine under the following conditions.
• a salt spray test was carried out on the drawn surface of the cups according to JIS Z-2371. The testing time taken until white rust occurred was measured.
• the lubricating resin coated steel strips falling within the scope of the present invention show excellent continuous formability and lubricity during high-speed press forming, leaving little or no powder after working. They also show good post-working corrosion resistance.
• Lubricating resin coated steel strips designated sample Nos. 201 to 220 were prepared under the following conditions.
• Resin coatings were formed by substantially the same procedure as in Example 1 except that the compositions reported in Table 3 were applied.
• sample Nos. 221 to 234 were prepared by the same procedures as above except that some parameters were outside the scope of the present invention. Plated steel strips were subjected to chromate treatment and coating dispersions having the composition reported in Table 3 were then applied to both the surfaces of the chromated strips to form resin coatings in the coating weights reported in Table 3.
• the lubricating resin coated steel strips falling within the scope of the present invention show excellent lubricity during high-speed press forming. They are fully resistant to corrosion both as formed and as worked.
• Lubricating resin coated steel strips designated sample Nos. 301 to 309 were prepared under the following conditions.
• Example 2 Substantially the same as in Example 1.
• the amount of chromate coating deposited was controlled to 50 mg/m 2 as Cr on each side by adjusting the spraying time.
• Two different coating compositions were prepared as reported in Table 5. One composition was applied to one surface of the chromated strips and the other composition was then applied to the opposite surface, both by roll coating. The coatings were dried at 150° C. for 40 seconds. A lubricant-containing resin coating was formed on the one surface and a lubricant-free resin coating was formed on the opposite surface. The amount of each coating applied was reported in Table 5 on a dry basis.
• sample Nos. 310 to 314 were prepared by the same procedures as above except that some parameters were outside the scope of the present invention. Plated steel strips were subjected to chromate treatment and coating dispersions having the composition reported in Table 5 were then applied to the opposite surfaces of the chromated strips to the coating weights reported in Table 5. Some samples had lubricant-containing resin coatings on both the surfaces and the remaining samples had lubricant-free resin coatings on both the surfaces.
• Example 2 Substantially the same as in Example 1. During drawing, the coated strip was placed on the die such that the lubricant-containing resin coating was on the die side. The blank holder pressure was increased to 3 ton.
• the test was substantially the same as in Example 1 except that the blank holder pressure was increased to 3 ton.
• the lubricating resin coated steel strips falling within the scope of the present invention show excellent lubricity during high-speed press forming. Deep drawability is satisfactory. They are fully resistant to corrosion both as formed and as worked.
• the present invention in the first form provides surface-treated steel strips having high lubricity during high-speed press forming and thus featuring continuous press forming. They can be readily press formed without the need for lubricant like press oil. They are also resistant to stains as by finger prints during handling.
• the present invention in the second form provides surface-treated steel strips having improved corrosion resistance and exhibiting high lubricity during high-speed press forming. They can be readily press formed without the need for lubricant like press oil. They are also resistant to stains as by finger prints during handling.
• the present invention in the second and third forms provides surface-treated steel strips which develop little rust during the period between their manufacture and actual working by the user.
• the lubricating resin coated steel strips of the invehtion allow the user to omit the lubricant oil applying step which is necessary for facilitating smooth press forming and must be followed by degreasing in the prior art, contributing to a cost reduction.

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